Automatic control systems for hydrofoils



Aug. 25, 1964 H. VON SCHERTEL 3,146,457

AUTOMATIC CONTROL SYSTEMS FOR HYDROFOILS Filed Dec. 10, 1962 2Sheets-Sheet 1 rs 9 Z "43 2a A :5' m. l I r- 15/ )z/ g- 25, 1964 i H.VON SCHERTEL 3,146,457 I AUTOMATIC CONTROL SYSTEMS FOR HYDROFOILS FiledDec. 10, 1962 2 Sheets-Sheet 2 United States Patent 3,146,457 AUTOMATICCONTROL SYSTEMS FOR HYDROFOILS Hanns von Schertel, 450 Sonnenberg,Hergiswil am fies, Switzerland Filed Dec. 10, 1962, Ser. No. 244,240 11Claims. (Cl. ILL-66.5)

The invention is concerned with an automatic control device, whichserves to maintain the depth of immersion of hydrofoils, which areattached to watercraft, as Well as for the reduction of rolling andpitching, and of the vertical accelerations of such craft at sea. It isapplied to foils, which have hinged flaps at their trailing edge forinfluencing of lift, and especially at such foils which during travelare submerged entirely below the watersurface.

As is well known, fully submerged hydrofoils are not autostable andthey, therefore, need an automatic control of lift in dependence ontheir immersion depth, in order to maintain the stability of the craft.In a heavy sea, control of immersion depth alone will not achieve asuflicient seaworthiness and performance, since, on the one hand, thefoil will try to follow the contour of the waves when cruising againstor transversely to the sea, a fact which will lead to great verticalaccelerations and to great rolling and pitching angles, and, on theother hand, the foil with the seas astern, will be unfavorablyinfluenced by the orbital motion, changing its angle of attack orincidence from time to time. When emerging from the wave crest, the foilwill be heaved considerably, so that it could easily come too close tothe water surface and thus suffer from aeration, while the lift willdiminish in front of the wave crest, so that the hull may enter orstrike the crests of the waves.

In the case of automatic control systems for maintaining the immersiondepth which have been known heretofore, the fully submerged hydrofoilhas been arranged to pivot about a transverse axis, or it has pivotedflaps along its trailing edge. The adjustment of the angle of attack ofthe foil or of the flap, respectively, is accomplished through controlelements which are sensitive to immersion either mechanically,hydraulically, or electrically. Feelers gliding on the surface of thewater are used as a mechanical control, which feelers are attached tolong forwardly projecting arms. Such control arrangements, however, havethe disadvantage that the feeler arms are bulky and are easily subjectto damage. Electronic arrangements are also known, where pairs ofelectrodes have been placed along the foil struts, which by galvanicaction will close a circuit whenever they are submerged. The number ofthe pairs of electrodes thus short-circuited equals an electric value inproportion to depth of immersion which by amplifiers and servo-motoreffects deflection of the flaps. Recently, sonic sensors have been usedto maintain the depth of immersion, which emit impulses or continuoussignals toward the water surface, and, in the case of deviations of thedesired height or flying altitude of the boat, bring about changes ofthe angle of incidence or attack of the foils, or of the flapsrespectively, in a corrective direction via electric and hydraulicamplifiers. Such electronic installations, which usually need twosources of energy, are extremely complicated, expensive and subject tobreakdowns, all of which detract from maintaining of stability.

This present invention will eliminate the disadvantages described, byadmission of air to the sub-pressure or low pressure regions of thefoils profile for the automatic operation of the foil flaps, the inflowof air being produced during travel by the sub-pressure generated by thewater flow on the foil or strut profile, and being changed 3,145,457Patented Aug. 25, 1964 with the help of a simple installation as afuction of the immersion depth, so that additional sources of energy arenot required, and a control system is provided which is distinguished byits surprising simplicity and dependability. In order to diminish thevertical accelerations the rolling and pitching angles and the influenceof the orbital movement, the sub-pressure could also be influenced bystill other control valves. The control system has no unwieldy elementsand those elements lying in the water are sturdy and are largely immuneagainst collision with driftwood.

The invention consists in connecting a piston or diaphragm in a cylindermeans, in a known manner, with the hinged flap at the trailing edge ofthe foil in such a manner that deflection of the flap is producedwhenever the piston or diaphragm is moved. An element producingsub-pressure conditions, which is equipped with suction apertures, and acontrol member which has air intake openings which are arrangevertically one over the other and which are located partially above andpartly below the normal surface of the water, are connected with theinernal space in the cylinder means. With increasing foil immersion, theincreasing sub-pressure will move the piston in the direction to cause apositive deflection of the flaps; that is to say, downwards. At the sametime, an air regulating valve is provided between the control member andthe cylinder means which valve can be influenced through any giveninstruments responsive to the movements of the boat in the seaway andwhich can also be connected with the steering system setting the courseof the craft.

The element producing the sub-pressure conditions may be formed by thestrut for the profiled foil, or by the upper surface of the foil, bothof which have suction apertures. The air intake orifices, with which thecylinder means are connected, could also be located above the normalsurface of the water, and the air intake openings located below theothers and which preferably should overlap with those above, could beseparately connected with air discharge openings on the upper side ofthe foil, in which case the flap would preferably have means for thelimitation of the deflections in the negative direction.

In order to make the hydrofoil immune against the orbital movementswithin the waves of the sea, that is to say in order to obtain thedeflections of the aps, which would balance out entirely or partiallythe fluctuations in lift as a result of the changes of the approachangle of the current, openings for sucking away of air which are locatedalong the upper side of the foil near its leading edge, can be connectedwith that space of a second operating cylinder in which the underpressure will move the piston in the direction of a negative deflectionof the flaps.

Other objects, advantages and capabilities of the present invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings, illustrating severalpreferred embodiments thereof.

In the drawings:

FIGURE 1 is a front elevation view of hydrofoils and control elements ofthe present invention, on the hull of a boat which has been shown incross section;

FIGURE 1a is a top plan view of the hydrofoils of FIGURE 1;

FIGURE 2 is a diagram of the control arrangement in section, wherein thesectional plane extends vertically and in cruising direction, which inthis case is from the left to the right;

FIGURE 2a is a horizontal section view taken along the line Za-Za ofFIGURE 2.;

FIGURE 3 is a diagram of a modified form control installation shown insection, similar to FIGURE 2;

FIGURE 4 is a further modification of the control arrangement shown insection;

FIGURE 5 shows the arrangement responding to the orbital movements inheavy seas in section, wherein the sectional plane runs the same way asin the preceding figures, the remaining elements of the control systembeing omitted;

FIGURE 6 shows a diagram of an arrangement responding to the inclinationof the waves in section as in the preceding figures, and FIG. 7 is avertical section view of a hydrofoil illustrating certain details of anexemplary flap construction.

The same elements in the various drawings are designated with the samenumerals.

in FIGURES 1 and la the fully submerged hydrofoils 1 are shown, which attheir trailing edges have hinged flaps 2 and which are attached to thehull 30 of a craft by means of struts 4. Instead of two divided foils,it would also be feasible to provide a continuous foil with dividedstarboard and port flaps. The most essential elements of the controlsystem are the suction openings 8' at the upper side of the foils. Thestruts 4 serve as a control member which has lateral air intake openingsand which, at the same time, as mentioned previously, serves as aconnecting support between the hull 39 of the craft and the foil 1. Afirst cylinder 9 and a second cylinder 23 are provided, the latter forbalancing of the orbital movements in the water. The other elements ofthe control system have been omitted in FIG- URE 1 for the sake ofclarity.

The plan of the control system is shown in FIGURE 2. The flap is hingedat the trailing edge of the fully submerged hydrofoil 1 by means of ahinge joint 3. The flap 2 is linked with the piston 11 of the firstcylinder 9 through a connecting rod 12. The foil 1 may have any desiredprofile.

The control member 4, formed by the strut, has a streamline-shapedprofile which can be developed as a symmetrical circular segmentprofile, or preferably with a parabolic head and a blunt trailing edge(see FIGURE 2a). In the leading portion at the side of the controlmember 4, where during cruising a strong sub-pressure area will developwherever the control member is submerged below the surface of the water,there are the air intake openings 6, which open intov ducts 5.

For the design according to FIGURE 2, the element producing thesub-pressure is formed by the lower part of the control member nearerthe foil, along which element an increased sub-pressure occurs as. aresult of the influence of the upper side of the foil.. There one orseveral suction openings 8 have been provided which open into thesuction channel 7. While cruising, air will be sucked away from thechannel 7 and from the space of the cylinder 9, connected with thechannel 7 via channel 7a through the sub-pressure developing within thecurrent, so that a low pressure will be produced in the cylinder spacewhich will exert a downward force on the piston 11.

On the other hand and in. addition, the cylinder space 1% is alsoconnected with the ducts 5 for the intake of air via the channels 7 and7a and the valve 14 and the conduits 13. Anyone of these channels, ofwhich one or any desired number may be provided, has a group of intakeopenings 6 arranged one above the other. The groups, as FIGURE 2 shows,are again arranged in the sequence of the channels, lying one above theother in such a manner that all of them together in a vertical directionform a continuous row of openings 6, which during cruising will liepartly above and partly below the surface of the water WL.

Air is sucked in through the openings 6 of the control member 4, locatedduring cruising above the surface of the water and, as a result, thesub-pressure in the channels and in the cylinder space It is decreasedin comparison to the sub-pressure existing along the suction openings 8.The openings lying underneath the surface of the water are closedagainst the entry of air by the waterflow causing a sub-pressure onthese openings which approximately balances out the sub-pressure alongthe suction openings 8. The sub-pressure which at times appears in thecylinder space ltl, will depend on the relationship of the totalcross-sectional area of the air intake openings to the constantcross-section area of the suction openings 8. Since the exposedcross-sectional area of air intake openings will change with the degreeof submersion of the control member 4, the sub-pressure in the cylinderspace it]: will also change as a function of the submersion. If the foil1 with the control member 4 increases its immersion depth, then thecross-sectional area for the entry of air will diminish and thesubpressure will increase until finally the same sub-pressure appears inthe cylinder space 10 as on the suction openings 8, whenever all entryopenings are submerged below the surface of the water. Conversely, thesub-pressure in cylinder space In will drop whenever the foil approachesthe surface of the water, until finally when all openings which havebeen provided will be free, atmospheric pressure will almost have beenreached. At the same time, one can gather from FIGURE 2 that the suctionopenings 8 and the entry openings 6 are connected with the internalspace of the cylinder 9, in which the sub-pressure will move the piston11 in the direction of the positive flap deflection, that is to saydownwards.

The force which, as a consequence of sub-pressure, has been exertedagainst piston 11 will be transferred to flap 2 as a moment around theaxis 3 through the rod system 12. Flap 2 on its part exerts a countermoment under the effect of the forces of flow. The flap-moment increasesabout linearly with the flap deflection. The moment created by the powerof the piston and the counter acting flap-moment will balance each otherout, so that to every magnitude of the sub-pressure in the space It),there corresponds a certain piston power and a certain flap deflectionwhich again, and approximately linearly with the angle of deflection,will influence the lift of the foil. Since according to what has beensaid before, the sub-pressure is a function of the extent of immersion,the resulting flap deflection and the lift also are functions of thesubmersion of the foil.

From this arrangement the following function will result for thecontrol:

If the foil leaves its normal position in cruising and if it increasesits depth of immersion, an increase in lift will be caused through apositive flap deflection which directs the foil back to its normalsubmerged depth. Conversely, an approach to the surface of the water iscorrected with a decrease of lift (negative flap deflection), so thattherefore the stability of the craft is insured at a correct selectionof the control values.

The process of control is largely independent of the speed, since boththe sub-pressure alongside the suction openings 8 as well as the flapmoment are a function of the speed, so that the condition oftheequilibrium between the piston power and the flap moment will not bedis- 'turbed in case of changes in speed.

For the sake of understanding the function of the control it must alsobe mentioned that all hollow spaces, which during cruising areventilated, will be filled with water when the craft is at a standstill.As soon as the craft begins to cruise, sub-pressure which will suck thespaces empty of air will develop along the suction openings 8 as well asalongside the air intake openings 6. The experiments have shown thatthis process requires only a few seconds. During cruising thesub-pressure always will remain alongside all openings, so that only attimes will very small quantities of water enter through the openingslying directly at the surface of the water where an almost atmosphericpressure exists. These small quantities of water however do not impairthe control.

FIGURE 2 shows that the air quantity regulating valve 14 has beenswitched into the connecting conduits 13 and 7 leading from the frontair intake ducts 5 to the rear suction channel 7. This valve has thepurpose of controlling additionally the quantity of air intake in order,thus, to influence the pressure in the cylinder 9 and the deflection ofthe flap 2. The quantity of air entering into this system, and thesub-pressure which will appear as a result, are therefore determined bythe superimposed commands of the control member 4 and of the airquantity regulating valve 14.

In the example given in FIGURE 2 the valve 14 has been developed as asliding valve member into which open the air intake ducts 5 of thecontrol member in such a sequence that the mouth of the flow duct,together with the uppermost group of holes, will be closest to the valvemember 15 and the rearmost ducts, with the lowest group of holes, willbe the farthest removed from the valve member. The valve member 15 inits middle position as drawn, will open up the passage from the airintake ducts 5 to the suction channel 7. As it is moved in one direction(to left), it will choke off and close the ducts 5, that is to say firstthe uppermost group of holes, then the middle group and finally thelowest group, while the valve member will additionally admit air throughthe intake slit 17 whenever it is operated in the other direction (tothe right).

The plurality of ducts 5, with groups of intake openings lying above oneanother, have been provided in order to achieve an even throttling ofthe quantity of air entering through valve 14. It is easy to understandthat when providing only one single channel into which all entry holesopen, and whose cross-sectional area of entry along the valve mustnaturally be equal to the total crosssectional area of all entry holes,a throttling of the quantity of air will occur only whenever thecross-sectional area of the throttling is smaller than the totalcrosssectional area of all intake openings which are above the surfaceof the water. Therefore, whenever the craft cruises, for example at thelevel indicated by the line WL, where approximately half of the openings6 will be opened, then half the path of the valve member will exert noeffect and throttling will start only after that. The sub-division ofthe three channels according to FIGURE 2 will result in a considerablymore even throttling effect. The uppermost group of holes of theforemost channel during cruising will lie above the surface of thewater, completely out of the water, so that here throttling will beginimmediately through the valve member 15, which will have as aconsequence a decrease in the submersion of the foil so that the middlegroup of holes of the middle channel too will be completely emergedwhenever the valve member has completely closed the foremost openingalong the valve. If now the valve member begins to close the entry ofthe middle channel, then here too a throttling of the quantity of airentering through the middle group of holes would occur immediately. Thevalve 14, therefore, will operate the more uniformly the more air intakechannels have been provided.

Without deviating from the system of valve control, the valve can alsobe developed as a rotary slide valve. Also, in order to achieve a moreeven supply of additional air, it will be possible to provide air intakechannels in the control member 4 in the same manner as prescribed andinstead of the free entry at point 17 said air intake channels open,into the air quantity control valve 14, one behind the other, instead ofthe intake slit 17. Whenever the valve member 15 is moved to the right,it will then open up the intakes for the additional air beginning withthe uppermost group of holes to the lowest group of holes.

In order to increase the sea worthiness of the craft controlled by theinstallation as described, to diminish the rolling and pitching and thevertical accelerations, the air quantity control valve 14 can beautomatically regulated through control devices, which react to themovements of the craft at sea, such as gyroscopes, accelerometers anddevices which will measure the submersion speed of the control member.

Such devices have been described in my earlier US. patent applicationS.N. 67,189, now Patent No. 3,117,546. In FIGURES 2 and 4 these deviceshave been indicated altogether by the number 20.

With the simultaneous application of several control devices for thecontrol of a foil or a part of the foil, such devices may each operate aseparate valve 14 and which together connected in parallel, areconnected with the operating cylinder of one foil. It would also bepossible that all devices would operate only one or perhaps two valvesby means of the known mechanical or hydraulic super positions. It mustbe stressed as an advantage of the control system, that the forces forthe operation of the air quantity control valve are extraordinarilysmall, so that the control devices can be connected directly with thevalve without interposing any amplifiers, a fact which provides anessential simplification and increase in the reliability of theoperation. Furthermore, through the described super position of thecontrol caused by the control devices, with the control of the submergeddepth, there is this further advantage, that in case the control devicesfail (which devices in this case may be arranged in such a way that theywill return to their middle position), the stability will still bemaintained just the same through the control member 4. The craft withfully submerged, slight- 1y dihedral foils bank outward when cruisingcurves because of the centrifugal force, and, through the lateralresistance of the struts occurring when the sliding movement isintroduced, a pair of forces will develop which banks outward. In orderto counteract this moment and in order to bring about an inward bankingin the curve, through an oppositely directed operation of the airquantity control valves of the starboard and port foil (see FIGURE 1)respectively of the two halves of the foils, additional air will bebrought in at the foil which is located on the inside of the curve,while the supply of air to the operating cylinder of the foil located onthe outside of the curve is being throttled. The operation of the valvestakes place corresponding to US. patent application SN. 67,189, nowPatent No. 3,117,546 in a guided manner, through a cam plate with spiralpassages which is coupled with a directional control (steering wheel), adriving means attached to a lever meshing or operatively connecting withsaid cam plate. The two connecting elements, one of which is shown at 18in FIGURE 2, lead towards the housing of the starboard and port airquantity control valve 14 which are movable in the bearings 19, saidhousing being arranged in such a manner that they will cause oppositecontrol effects at movement in the same direc tion. Through acorresponding form of the spiral at the cam plate, every desired courseof the transmission ratio between the turn of the steering wheel and thepath of the valve can be achieved. In order to make possible themovement of the valve housings, the conduits 13 are made of flexiblehose. The change of quantity of air which is brought about by the valve14 is, therefore, brought forth both by the operation of the valvemember 15, through the automatic control devices 20, as well as throughthe movement of its housing on the part of the course steeringoperation. The control arriving from both sides are superposed one overthe other.

The air quantity control valve 14 of each foil, or of each half of eachfoil respectively, will preferably be located inside the hull of thecraft as shown in FIGURE 1, where it is protected against entry of anywater or dust. Correspondingly all automatic control devices whichoperate the valve member of the valve 14 can also be located protectedinside the hull of the boat. In FIGURE 1 the operating cylinder 9 hasalso been located inside the hull of the boat with the help of a rockerarm 29, which takes 7 care of transferring the movement from thecylinder to the rod system 12.

In another exemplary form illustrated in FIGURE 3, the foil 1 forms themember creating the sub-pressure, said foil having suction openings 8'on the upper side of the foil. The openings. 8 are located on the rearpart of the foil profile inFIGURE 3, and they open into a channel 28,which runs obliquely through the foil and which in turn is connectedwithvalve 14.through the suction channel 7. The suction openings 8',according to FIGURE 1a may extend across only a part of the span widthof the foil (left side of the figure), or they may extend across thewhole span width corresponding to the right side of the figure. Sincethe lift of foils, whose upper side has air exit openings correspondingto US. patent application SerialNo. 67,189, can be regulated by changingthe quantity of air supplied through these exit openings, the lift ofthe foil according to FIGURE 3 is not only influenced through flap 2 butalso through the quantity of air emerging. from these suction openings8'. Such influencing extends in the case of the right hand foil ofFIGURE 1a, across the whole foil, and in the case of the left hand one,only across a part of said foil. The control process is also as follows:

Whenthe: quantity of. air flowing to the air exit openings 8" isincreased through the control member or the valve 14; the lift of thefoilwill decrease, but at the same time thepressure in the channels andin the cylinder space will decrease too. The deflection of the fiap willdecrease through this decrease of pressure in the negative sense, sothat the decreased lift of the foil will be brought about by both: the.change in the quantity of air supplied to the upper side of thefoil aswell as'through the swinging of the flap.f If thevolume of air flowingto the air exit openings 8' is throttled down, then conversely the liftof the foil, first of all in consequence of the smaller quantity of airemerging and secondly in consequence of the positive deflectionof theflap, will be increased.

The FIGURE 3 shows another design of the cylinder 9 which. in this case,has been developed in the preferred shape as a rollerdiaphr-agmacylinder and has complete water tightness with very lowfrictional forces, factors which for. the response sensibility of thedevice would be of significance. The transfer ofv the piston movement tothe flap inFIGURE3 takes place by means of a rod'which r-uns protectedinside of'the strut 4. The rod can be made with a very small quantity ofmaterial, a factor which is favorablefor achieving a great reactionspeed of the control system.

In the practical example shown in FIGURE 4, the member producing thesub-pressure, as in FIGURE 2, is formed by the lower part of the strutwhere the suction openings 8' are located. The suction side of the foil,however, also has air suction openings 8' as in FIGURE 3, whereby thearrangement is made in such a manner that the; influencing of the lifttakes place, not simultaneously through: the flap and the supply of air,but in sequence. For this purpose the air entry openings 6 of the duct 5with which the operating cylinder 9 is connected through channel 7", areplaced above the normal surface of the water WL, while theair entryopenings 6' of the duct 5', which have been arranged to lie below thetop ones, are connected through a, separate conduit 7 with the air exitopenings 8' on the upper side of the foil. The upper air entry openings6 for the operating cylinder 9 preferably overlap in, their position asto. height, with the air entry openings 6' for the upper side of thefoil. The flap is preferably provided with a stop in order to limit thedeflections in the negative direction, for example as in FIGURE 4, wherethe piston 11 joins the upper cylinder cover whenever the flap tands inthe middle position as illustrated.

Just as in the preceding examples, one air quantity controlval've 14 or1.4, corresponding to the tWo separate circuits, has been inserted inthe connecting conduit running from the entry ducts 5 or 5,respectively, to the 1 a negative flap deflection.

8 suction channels 7 or '7', respectively. The two valves are connectedwith one another to co-ordinate their motion and they are operatedtogether through the rod 16. They can, as shown in FIGURE 4, be arrangedin such a manner that the entry of air to the two circuits is throttleddown or enlarged simultaneously or else in such a manner that thethrottling down of air moving to the foil takes place first before adeflection of the flap will be brought about through throttling down ofair to the operating cylinders. For this purpose the mouth of the duct 5in the left valve 14 must he moved to the left and, at the same time, asufiiciently large path must be allowed for both valves. Also, thevalves may be arranged in such a manner that the additional air will befirst supplied to the operational cylinder, that is to say, first theflap is put in its zero position, before any additional air can emergealong the foil. In this case it will be necessary to move the air entryslit 17 of the right valve 1 toward the right and the two valves must begiven a correspondingly greater path.

in this design the medium and the lower lift areas are controlledthrough the supply of air along the foil, While the high liftcoetficients will be achieved through the flap deflections afterventilation of the foil has been closed down. T he described overlappingof the rows of holes serves the purpose of bridging the response time ofthe.

flap in order to obtain at the same time, with the submersion andclosing down of the uppermost opening for the air supply to the upperpart of the foil, a flap reaction and with it a steady course of theincrease of lift.

In addition, FIGURE 4 shows the damper 33 of a known design, whichserves. preventing or restraining the swings of the flap. The piston 34is connected with the piston 11 of the operating cylinder. In apreferred design, the damper has an overflow channel 35 with a checkvalve 36, which will permit free passage of the liquid when the pistonmoves up, which however will close down in the direction of movement ofthe increasing positive flap deflections, so that the damping willoccur. Through this arrangement a quick reaction of the flap will beguaranteed whenever the foil approaches the surface of the water, whichfact brings with itself the danger of a foil aeration.

In FIGURE 5 the second operating cylinder 23 for v the flaps 2' isvisible, whose space 24 is connected with the air suction openings 27through the line 26 which is 10-- cated. on the upper side of the foilin the vicinity of the leading edge. The space 24 is located onthat sideof the piston at which the sub-pressure acts in the direction or" Thepiston 25 has a smaller diameter than the main piston 11, so that duringnormal cruising conditions a constant force acts against the positivedirection of the main piston. The piston 25 at great emersion, when onlythe lowest or no air entry opening 6 of the control member 4 will belocated below the surface of the water, and the sub-pressure upon thepiston 11 becomes small, will force the flap to negative deflections.

The sub-pressure at the leading edge of the foil profile Where thesuction openings 27 are located, changes considerably with the directionof the flow against the profile and, to be sure, increases with anincrease in the angle of incidence. If, therefore, in the orbitalmovement of the waves a lift increase of the foil occurs as a result ofthe enlargement of the angle of incidence, then at the same time thesub-pressure on the piston 25 will increase and the flap is moved in anequalizing sense in the direction of negative deflections. If,conversely, the orbital movement decreasesthe angle. of incidence andlift, then the force acting upon the piston 25 will also'be decreasedand the main piston will increase the deflection of flap 2.

In order todecrease the speed of response of the control system upon thechanges in immersion of the control member 4, which from time to time isdesirable in order to suppress a reaction to short waves, the channel 7or the cylinder space, respectively, are connected with an air space 21which is changeable as to volume (FIGURE 2). In the example, the changeof volume is accomplished through movement of the piston 22. Instead ofthe smooth change, the increase of volume can also take place step bystep by connecting one or several unvariable spaces, perhaps of variedsize.

It is understandable that with the growing volume of air between thesuction elements and the operating cylinder an increased dampening ofthe variations of pressure in the sea occurs and that the device permitsan adaptation to each period of encountering specific wave crests.

In FIGURE 6 a design of the control arrangement has been shown whichresponds to the slope of the waves and, thus, acts in the way of apre-control means. In this case, an additional auxiliary control member4a with the air entry openings do has been attached at a distance behindthe control member 4. The auxiliary control member 4a is connected withthe second operating cylinder 23 through a conduit, the piston 25 ofsaid operating cylinder responding to changes of the orbital angle.Under the effect of the control member 4a, the reaction of the piston 25remains unaffected by changes of the angle of incidence against themember 4a, however, the control system responds also to inclinations ofthe water surface as follows:

In the case of changes in immersion with a parallel keel, the controlsystem acts in the same sense as described before because the changes inforce which occur along the main piston 11 outweigh those of theauxiliary piston 25. If the boat dips into a wave with an inclination ofWLl, or if it will suffer a heavy trim by the bow, then the sub-pressureon the main piston will rise in consequence of the decrease of the areaof air entry in the control member 4, while the counter force exerted bythe auxiliary piston 25 will drop in consequence of the emersion of theentry opening 6a of the control member do, so that a great positive flapdeflection will occur along foil 1. It is easy to understand that thisdeflection is essentially greater than will be reached in the case of aparallel increase of immersion, because in the latter case the counterforce upon the piston 25 increases. The deflection angle will become thelarger the greater the inclination of the waves. If, for example, in thewake when cruising through the crest of a wave, a diminishment of theangle of incidence occurs on the basis of the orbital movement, then thesub-pressure exisiting along the suction openings 27 will drop, whichhas as a consequence a further decrease of the force exerted on piston25 and thus a further enlargement of the flap deflection. On the surfaceof the water WLZ, a negative deflection of the flap will take placewhich assumes even greater negative values, in correspondence with whathas been said before, if for example an enlarged angle of incidence willoccur along the front of the wave of following sea. It is self-evidentthat a third operating cylinder, for the control of the inclination ofthe waves with the suction point 27a of its own, can be provided insteadof the cylinder 23 responding to the orbital movement. Such anadditional suction point could be provided, for example, along the lowerend of the auxiliary control member 4a or along the streamlined body 31,which is located at the end of said auxiliary member.

Subsequently some more partical design of the parts of steeringarrangement will be described:

The air entry openings 6 can be circular or slit-shaped and they can beeither on one side or, for the sake of greater security, on both sidesof the strut, so that if the air should perhaps rush in, only half thesubmerged openings will be disturbed at any particular time on one sideof the support.

The submersion characteristics of the hydrofoil (the course of theincrease of the flap-angle and of the lift during submersion) isdetermined by the vertical distribution of the sectional area of the airentry across the control member, therefore, by the size and the distancefrom one another of the entry openings 6. This characteristic can bechanged in order to adapt the behavior of the craft to the prevailingsea, whenever the control member for this purpose, has two or severalchannels with rows of variable openings, which according to choice, canbe connected through a valve with the cylinder space. If the channel inaction is equipped with a series of large distances of the openings fromone another then the lift will only change little with the depth ofsubmersion (small stability for cruising in short waves) whereas withsmaller distances, a greater stability and a stronger adherence of thefoil to the contour of the wave will develop.

Especially when using roller-membrzine-cylinders, whose membranes areexposed to possible damage, it would be possible-in order to increasethe safety of the control arrangement-40 use two or even severaloperating cylinders into whose supply-conduits known by-pass valves havebeen built in, which would cut off the damage cylinder, wheneversub-pressure will drop in said cylinder as a result of the entry of air,and through this a difference in pressure between the cylinders wouldappear.

Since the sub-pressure along the upper side of the foil and along thestruts is relatively small, and naturally at the maximum could onlyreach the complete vacuum, large diameters for the operating cylinderswill result. They can be decreased through switching in of pressuretransformers of a known kind between the element producing thesub-pressure and the operating cylinder. Through these devices, thesub-pressure carried to them, increased many times into super pressure(positive pressure), will be carried further to the operating cylinder9. Correspending to the pressure reversal the pressure conduits towardthe appropriate opposite sides of the piston are led as in FIGURE 2. Thesuper pressure in the device will change proportionally to thesub-pressure supply. The pressure transformers must be fed compressedair which is produced by compressors, the disadvantage of the pressurereduction consisting in this.

Another method to attain a smaller diameter for the operating cylindersconsists in the diminishment of the flap moment through the design ofthe flap as shown in FIGURE 7. The pivot axes 3 of the flap 2, in thisinstance, are removed from the leading edge of the flap so far, that thepart 32 which is located in front of the axis, serves as an unloadingsurface for the reduction of the flap moment. In other words the axis 3has been moved up closely to the center of lift of the flap. Whenswinging the flap, the front part 32 carries out the movement ascompared to the fixed profile of the foil. The leading edge of the flapis narrower than the back wall of the fixed profile of the foil, so thatin the middle position of the flap (solid line) a step will developabove and below. However at the greatest positive deflection, the upperpart of the flap is alined with the upper part of the profile (dottedline) and at the greatest negative deflection, the lower side of theprofile is alined with the underside of the flap. If the air suctionopenings 8 are provided directed rearwardly into the upper step, thenthis will result in a favorable arrangement, where the suction openingsat negative deflection angles at which great quantities of air willexit, are completely opened but which, with increasing positivedeflection and a decreasing quantity of air, will close down more andmore, finally completely closing at the greatest positive deflectionwhere no more air will escape. The suction side contour of the profilethen will have no more non-uniformity.

In the case of water craft, where the control system according to theinvention is being applied, bow foils only, which are attached to theforepart of a ship, for example, corresponding to FIG. 1, may beprovided with the control system, while the stern foil may be rigid andhave no flap, and remain uncontrolled. This stern foil will maintain itssubmerged depth automatically through the fact that every change insubmerged depth which it will experience is associated with rotation ofthe craft about the front foils which are kept constant in theirsubmerged depth, a fact Which has as a consequence a change of the angleof attack in a recovery sense. In order to be more effective indecreasing the pitching vibrations, the stern foil can be provided witha flap whose operating cylinder however will only be influenced by theinstruments responding to inclinations and accelerations, that is to sayno control member for the stern foil has been provided and the entry ofair is solely controlled by an air quantity regulating valve operated bythe instruments.

Naturally this control system can also be used in the case of partiallyemerging foils of smaller dynamic stability.

While several modifications have been illustrated and described, it willbe apparent that other variations may be made within the spirit of theinvention, and it is desired therefore, that only such limitations beplaced on the invention as are imposed by the prior art and set forth inthe appended claims.

What is claimed is:

1. Apparatus for automatically controlling the immersion depth ofhydrofoils supporting a hull of a Watercraft and having at least onefiap hinged to the trailing edge or the hydrofoil, comprising cylindermeans having a piston therein, linkage means interconnecting said flapwith said piston for pivoting said flap about a hinge axis thereforresponsive to pressure changes in said cylinder means, sub-pressuregenerating means communicating with said cylinder means for subjectingsaid piston to sub-pressure conditions produced thereby to effectmovement of the piston in a positive flap deflection directionresponsive to increasing sub-pressure, control means for modifying saidsub-pressure conditions applied to said cylinder means including airducts connected with said cylinder means and having air intake openingsdisposed to occupy positions above and below the normal waterline whenthe watercraft is in motion for changing said sub-pressure conditionsapplied to said piston in relation to changes in the level of the airintake means relative to the water surface, and an air regulator valvebetween said control means and said cylinder means for variablyrestricting communication of air and admitting additional air from saidcontrol means to said cylinder means.

2. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, wherein a supporting strut is providedfor said hydrofoil ex tending from the watercraft to the hydrofoil, andwherein said sub-pressure generating means is formed in said strut bygenerally vertically extended air channel means projecting downwardly toa location adjacent to the hydrofoil, said air channel means havingsuction openings in a lower region thereof, which remain constantlysubmerged, opening through surface portions of the strut where suctionconditions are produced by movement of the strut through the water.

3. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, wherein said sub-pressure generatingmeans. is formed in the hydrofoil by air channel means therein havingsuction openings along. the upper side of portions of the hydrofoilwhere suction conditions are produced by the hydrofoil configurationduring movement of the same through the water.

4. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, wherein said air intake openings of saidcontrol means connected with said cylinder means lie above normalwaterline and air intake openings of said control means which lie belowthe normal waterline separately communicate with means along the upperside of the hydrofoil having suction openings and stop means for saidpiston limiting the deflection of the flap in a negative direction.

5. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, where in said control means comprises aplurality of separate air ducts, each having a group of air intakeopenings therein located in vertical array, said ducts being spacedalong the direction of travel of the watercraft, and the air intakeopening region thereof being located at different levels.

6. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, wherein said control means comprises aplurality of separate air ducts, each having a group of air intakeopenings therein located in vertical array, said. ducts being spacedalong the direction of travel of the watercraft, and the air intakeopening regions thereof being located at different levels, saidsub-pressure generating means including a vertical air suction channelterminating in suction openings located continuously below the waterline in suction pressure zones created during movement of thewatercraft, communicating duct means common to all of said ducts of saidcontrol means extending from the forwardmost of said ducts to therearmost of said ducts and said air suction channel, and said regulatingvalve having a valve member in said communicating duct for terminatingcommunication with said cylinder means progressively from the foremostduct to the rearmost duct and for admitting additional air to saidcylinder eans.

7. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, wherein a supporting strut is providedfor said hydrofoil extending from the watercraft, said control meansbeing formed of a plurality of generally parallel, vertically elongatedair ducts projecting downwardly in said strut to locations spacedselected distances above the hydrofoils in the lower ends thereof, theair intake openings in said air ducts being located at progressivelylower levels progressing from the front to the rear of said strut andthe air intake openings in adjacent air ducts overlapping each other aselected extent, an elongated manifold duct communicating with the upperends of each air duct and with said cylinder means, and said airregulating valve having a valve member movable in two directions axiallyof said manifold in one direction to progressively close off the upperends of said air ducts from communicating with said cylinder means in aprogressing manner from the forwardmost air duct to the rearmost airduct and in the other direction to admit additional air to said cylindermeans.

8. In apparatus for controlling the immersion depth of hydrofoils, thecombination in claim 6, wherein the air intake openings in said ductsare at progressively lower levels progressing from the forwardmost ductto the rearmost duct.

9. In apparatus for controlling the immersion depth of hydrofoils, thecombination in claim 1, wherein a damper cylinder having a piston and anoverflow duct from one side of the piston to the other is coupled tosaid cylinder means, said overflow duct having a check valve thereinoperative to close the overflow duct opening upon movement of the pistonof said cylinder means in the direction of increasing positive flapdeflection.

10. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, wherein a second cylinder having areciprocative piston is in communication with the first mentionedcylinder means, said second cylinder and piston having a relativelysmaller diameter than said first-mentioned cylinder means, air ductmeans having air suction openings located on the upper side of thehydrofoil adjacent to the leading edge thereof communicating with saidsecond cylinder to apply sub-pressure to the piston thereof in asenset'o cause the piston of said first-mentioned cylinder means to movein the direction of negative flap deflection.

11. In apparatus for controlling the immersion depth of hydrofoils, thecombination recited in claim 1, Wherein a second cylinder having areciprocative piston is in communication with the first mentionedcylinder means, said second cylinder and piston having a relativelysmaller diameter than said first-mentioned cylinder means, air ductmeans having air suction openings located on the upper side of thehydrofoil adjacent to the leading edge thereof communicating with saidsecond cylinder to apply sub-pressure to the piston thereof in a senseto cause the piston of said firstmentioned cylinder means to move in thedirection of negative flap deflection and a second References Cited inthe file of this patent UNITED STATES PATENTS 2,709,979 Bush et al. June7, 1955 FOREIGN PATENTS 549,266 Italy Oct. 9, 1956

1. APPARATUS FOR AUTOMATICALLY CONTROLLING THE IMMERSION DEPTH OFHYDROFOILS SUPPORTING A HULL OF A WATERCRAFT AND HAVING AT LEAST ONEFLAP HINGED TO THE TRAILING EDGE OF THE HYDROFOIL, COMPRISING CYLINDERMEANS HAVING A PISTON THEREIN, LINKAGE MEANS INTERCONNECTING SAID FLAPWITH SAID PISTON FOR PIVOTING SAID FLAP ABOUT A HINGE AXIS THEREFORRESPONSIVE TO PRESSURE CHANGES IN SAID CYLINDER MEANS, SUB-PRESSUREGENERATING MEANS COMMUNICATING WITH SAID CYLINDER MEANS FOR SUBJECTINGSAID PISTON TO SUB-PRESSURE CONDITIONS PRODUCED THEREBY TO EFFECTMOVEMENT OF THE PISTON IN A POSITIVE FLAP DEFLECTION DIRECTIONRESPONSIVE TO INCREASING SUB-PRESSURE, CONTROL MEANS FOR MODIFYING SAIDSUB-PRESSURE CONDITIONS APPLIED TO SAID CYLINDER MEANS INCLUDING AIRDUCTS CONNECTED WITH SAID CYLINDER MEANS AND HAVING AIR INTAKE OPENINGSDISPOSED TO OCCUPY POSITIONS ABOVE AND BELOW THE NORMAL WATERLINE WHENTHE WATERCRAFT IS IN MOTION FOR CHANGING SAID SUB-PRESSURE CONDITIONSAPPLIED TO SAID PISTON IN RELATION TO CHANGES IN THE LEVEL OF THE AIRINTAKE MEANS RELATIVE TO THE WATER SURFACE, AND AN AIR REGULATOR VALVEBETWEEN SAID CONTROL MEANS AND SAID CYLINDER MEANS FOR VARIABLYRESTRICTING COMMUNICATION OF AIR AND ADMITTING ADDITIONAL AIR FROM SAIDCONTROL MEANS TO SAID CYLINDER MEANS.